1. Field of the Invention
This invention relates to an elastic filament formed from a spandex polymer derived from a hindered polyester, an organic diisocyanate and an aliphatic diamine chain extender. The invention particularly concerns such a filament wherein the polyester is derivable from 2,2-dimethyl-l,3-propane diol (neopentyl glycol) and 1,12-dodecanedioic acid. The spandex filaments of the invention have improved resistance to degradation by mildew attack.
2. Description of the Prior Art
Elastic filaments of polyester-based spandex polymer can be prepared from a hydroxyl-terminated polyester which is capped with an organic diisocyanate and then reacted with an aliphatic diamine chain extender. The polyester forms what is called the "soft segment" of the polymer; the diisocyanate and diamine form the so-called "hard segment". The polymer can then be formed into filaments or films by known techniques. For example, filaments may be formed by dry spinning. Many such polyester-based spandex filaments are known. Some have enjoyed considerable commercial success, but their value could be further enhanced by certain improvements. For example, in swim-wear fabrics, although such filaments usually have adequate resistance to attack by swimming-pool chlorine, the filaments often degrade because of mildew attack. Accordingly, an object of the present invention is to provide a polyester-based spandex filament that has satisfactory elastic and tensile characteristics and satisfactory chlorine-resistance, but that also resists degradation caused by mildew attack.
Many hydroxyl-terminated polyesters made from .alpha.,.omega.-dicarboxylic acids and glycols have been disclosed for use in making the polyester-based spandex polymers. Generally, a preference is disclosed for acids that contain ten or fewer carbon atoms. However, none of the disclosures address the problem of mildew resistance or specifically mention poly(2,2-dimethyl-1,3-propane dodecanedioate) as a soft segment of a polyester-based spandex filament.
For example, U.S. Pat. Nos. 3,009,762 (Kohrn et al) and 3,009,765 (Slovin et al) disclose such hydroxyl-terminated polyesters derived from glycols and saturated organic dicarboxylic acids, the glycols and acids each having from 4 to 20 carbon atoms. These patents disclose that preferred polyesters precursors have a molecular weight of 1500 to 3000 and an acid value of less than 1. An acid value of 1 is equal to a glycol acidity of about 17.6 milliequivalents per kilogram (meq/kg). Among the polyesters specifically mentioned, though not exemplified, is a hindered polyester, poly(neopentyl sebacate).
U.S. Pat. No. 3,097,192 (Schilit) discloses elastic filaments of polyester-based spandex polymers and states that when the ester function is hindered, as with polyesters made with 2,5-hexane diol or 2,2-dimethyl-1,3-propane diol, the hydrolytic stability of the polymer is enhanced. In Examples II and IX, Schilit discloses a polyester-based spandex filament made with a polyester soft segment formed from sebacyl chloride and 2,2-dimethyl-1,3-propane diol. However, the tensile and elastic characteristics of the disclosed filaments are clearly in need of significant improvement.
Among the many other patents that disclose hydroxyl-terminated polyesters for segments of spandex filaments are U.S. Pat. Nos. 2,621,166 (Schmidt), 2,956,961 (Kibler et al), 3,211,701 (Muller et al), 3,481,905 (Weiden et al), 3,496,144 (Kunde et al), 3,506,617 (Collardeau et al) and 3,907,863 (Voss).
From a practical standpoint, some degradation of the spandex filament from mildew attack can be tolerated without it being objectionable to users of fabrics containing the filaments. However, the utility of the polyester-based spandex filaments would be much improved by increases in their mildew resistance.